Scientists Discover the Brightest Supernova Ever Recorded

A cosmic explosion 200 times more powerful than a typical supernova has left scientists speechless, and not just because of its breathtaking beauty.

At its peak intensity, the explosion - called ASASSN-15lh- shone with 570 billion times the brightness of the sun and was twice as luminous as the previous record-holding supernova. This record-breaking blast is thought to be a prime example of a superluminous supernova, a recently discovered and incredibly rare variety of explosion unleashed by certain stars when they die. What sorts of stars create this explosion remains a mystery.

ASASSN-15lh is amongst the closest superluminous supernovae ever beheld, at around 3.8 billion light years away. It's also the most powerful discovered in human history, says Subo Donng, lead author of the Science magazine study on ASASSN-15lh. "The explosion's mechanism and power source remain shrouded in mystery because all known theories meet serious challenges in explaining the immense amount of energy ASASSN-15lh has radiated."

But, by examining the bright, slowly fading afterglow the explosion emitted, astronomers have acquired a few basic clues about its origin.

Using an 8-foot telescope in Chile, Dong's colleagues took the first spectrum of ASASSN-15lh in order to identify the signatures of chemical elements scattered by the explosion. The spectrum the team found puzzled them, as it did not resemble any of the spectra from the 200 supernovae they had discovered to date.

Dong speculated that this was because ASASSN-15ih might in fact be a superluminous supernova. He tested his hypothesis by finding a close spectral match for the explosion in a 2010 superluminous supernova, and confirming ASASSN-16lh's distance. "The ongoing observations have further revealed that ASASSN-15lh bears certain features consistent with 'hydrogen-poor' super luminous supernovae (Type 1)." Just like other Type 1's, ASASSN-15lh has shown a steady rate of temperature decrease and radius expansion. However, it is way hotter than its closest supernova relatives, and, unlike most superluminous supernovae which have all burst forth from small, dim galaxies, its galaxy of origin seems to be bigger and brighter than even the Milky Way.

One of the best hypotheses about superluminous supernovae's incredible energy is that it comes from highly magnetized, rapidly spinning neutron stars called magnetars, which are actually the leftover hyper-compressed cores of massive, exploded stars. But ASASSN-15lh is so potent that this scenario falls just short of the required energies. Instead, a supernova of this magnitude might be triggered by the demise of incredibly massive stars that go beyond the top tier of masses that most astronomers would think are even attainable.

In order to discover more about ASASSN-15lh, and solve some of the mysteries surrounding it, Dong and his team have been granted time on the Hubble Space Telescope. With Hubble, they can obtain the most detailed views yet of the aftermath of the stunning explosion.

"The honest answer is at the point that we do not know what could be the power source for ASASSN-15lh," says Dong. "ASASSN-15lh may lead to new thinking and new observations of the whole class of superluminous supernova, and we look forward to plenty more of both in the years ahead."